Zinc electroplating process and electrolyte therefor

ABSTRACT

This invention relates to a method of producing bright zinc electrodeposits over a wide current density range, free of &#39;&#39;&#39;&#39;spores&#39;&#39;&#39;&#39; and/or striations, which comprises passing current from an anode to a metal cathode for a time period sufficient to deposit a bright zinc electrodeposit upon said cathode; the current passing through an aqueous bath composition containing at least one zinc compound providing zinc ions for electroplating zinc, A. AT LEAST ONE BATH SOLUBLE SURFACTANT SELECTED FROM THE GROUP CONSISTING OF BATH SOLUBLE POLYETHERS, SUBSTITUTED POLYETHERS, AND SUBSTITUTED NON-AROMATIC NITROGEN HETEROCYCLIC SURFACTANTS, AND B. AT LEAST ONE AROMATIC, NON-CARBONYL CONTAINING NITROGEN HETEROCYCLIC COMPOUND.

[ June 28, 1974 Unite States Patent [191 Harhulak [54] Z HNC ELECTRORLATING PROCESS AND ELECTROLYTE THEREFOR [75] Inventor: Edward Paul Harhulak, Allen Park,

Mich.

[73] Assignee: M & T Chemicals Inc., Greenwich,

Conn.

[22] Filed: Sept. 26, 1972 [2]] App]. No.: 293,659

[52] US Cl 204/55 R [51] int. Cl. C23b 5/10, C23b 5/12, C23b 5/46- [58] Field of Search 204/55 R, 55 Y, 43 Z, 44

[56] References Cited UNITED STATES PATENTS 2,451,426 lO/l948 Bair ct al. 204/55 Y 3,296,105 l/l967 Rushmere 204/55 Y 3,594,291 7/l97l Todt et al. 2.04/55 R 3,655,534 4/1972 Kampe 204/55 R 3,669,854 6/1972 Harbulak 204/55 R 3.730.855 5/1973 Poor ct al. 204/55 R Primary Examiner-G. L. Kaplan Attorney, Agent, or Firm-Kenneth G. Wheeless; Robert P. Auber; Robert Spector 5 7] ABSTRACT This invention relates to a method of producing bright zinc electrodeposits over a wide current density range, free of spores and/or striations, which comprises passing current from an anode to a metal cathode for a time period sufficient to deposit a bright zinc electrodeposit upon said cathode; the current passing through an aqueous bath composition containing at .least one zinc compound providing zinc ions for elec- 18 Claims, No Drawings ZINC ELECTROPLATING PROCESS AND ELECTROLYTE This invention relates to the electrodeposition of bright zinc, and is especially useful for plating from non-cyanide baths. More particularly this invention relates to improved zinc plating bath compositions, to methods of using and preparing such bath compositions and to improved surfaces having bright zinc'electrodeposits thereon.

The enactment and enforcement of various environmental protection laws, especially those designed to improve water quality, have made it desirable to significantly reduce or eliminate the discharge of cyanides, phosphates, and a number of metal ions from the effluents of electroplating plants. As a result, nompolluting bright zinc plating processes have been sought as alternatives to the classical zinc cyanide baths.

Alkaline solutions containing complex compounds of zinc and alkaline metal pyrophosphates have been proposed as a replacement for cyanide baths and cyanide processes for the electrodeposition of bright zinc. The electrodeposition of zinc using a pyrophosphate bath, however, may give relatively poor low current density coverage, spore" formation, roughness, insufficient brightness, and relatively non-uniform deposits. In addition, passivation of the anodes may produce undesirable precipitates which in turn can clog filter systems and sometimes results in intermittent operation necessitated by frequent changes of filter media.

The use of phosphates may also produce waste disposal problems since phosphates are not easily removed and may promote the growth of undesirable aquatic plant life if discharged into streams. These disposal disadvantages further limit the acceptance of pyrophosphate zinc plating bath compositions in industrial applications.

Non-cyanide zincate zinc plating baths have also been proposed as substitutes for cyanide containing systems. However, the bright plating current density range of these baths is quite limited, making the plating of articles of complex shape difficult, if not impossible. Since the addition of cyanide to these non-cyanide zincate baths greatly improves the bright plate current density range of the deposits, platers tend to add cyanides to their zincate systems, thus negating the noncyanide feature of the original bath.

Highly acidic zinc plating baths have been known for some time and such baths are cyanide-free. These systems do not produce bright decorative deposits, (in the currently accepted usage of the word bright), have extremely poor low current density coverage and find their chief application in the strip line plating of wire and sheet steel using very high but narrow current density ranges. Thus, they are not suited for plating objects of complex shape or for normal decorative, or rustproofing application.

More recently, neutral, mildly alkaline or mildly acidic noncyanide zinc plating baths containing large amounts of buffering and complexing agents to stabilize both pH and solubilize the zinc ions at the pH values involved have been employed to overcome the objections of using cyanide-based zinc plating processes. In general these zinc baths consist of an aqueous solution containing at least one simple zinc salt, (for example zinc sulfate, zinc chloride, zinc acetate), and an ammonium salt (for example an ammonium halide, or ammonium sulfate). The zinc bath may additionally contain an organic zinc complexing agent such as a hydroxy carboxylic acid or salts thereof, ethylenediamine tetraacetic acid or salts thereof, and/or similar materi als to prevent the precipitation of zinc from the bath as' 50 g/l gll 60 g/l ZnCl, NH,CI Citric Acid NH4OH to adjust the pH to some value between eg 4 and 8. Suitable bath soluble polyoxyalkylene surfactant 6 gll in order to improve and increase the brightness, luster and throwing power of zinc deposits from these baths, certain organic aromatic carbonyl compounds are generally used as brighteners. While these brighteners provide generally satisfactory zinc deposits from freshly prepared zinc baths, the deposits tend to be dull in low current density regions. In addition, because of the nature of the aromatic organic additives used as brighteners, highly objectionable oily decomposition products may form on prolonged bath electrolysis. These oily materials are not soluble in the bath and float on the surface where they adhere to parts as they are placed in and removed from the bath causing pitting problems during the plating cycle, with blotching and non-uniform results in subsequent chromate posttreatment of the zinc deposits. Removal of these oily decomposition products is difficult and troublesome,

and as a result zinc electroplating processes of this type have found only limited acceptance in the plating industry.

While mildly acidic, neutral, and/or mildly basic zinc plating baths of the type described above have the potential for producing suitable bright zinc deposits, the inclusion in their composition of organic complexing agents such as hydroxy carboxylic acids, and/or salts thereof, ethylenediamine tetraacetic acid and/or salts thereof, as well as other complexing agents makes it extremely difficult and expensive to remove zinc metal ions from these electroplating bath waste effluents. As a result, in the current state of the art of bright zinc electroplating from non-cyanide zinc baths, the use of organic complexing agents is avoided.

The exclusion of organic metal complexing agents from bright zinc electroplating baths has made it possible to effectively and easily remove zinc metal ions from plating plant waste effluents in compliance with anti-pollution laws. However, with the elimination of organic complexing agents it is desirable to operate the zincbath in the mildly acidic pH range, and it is more difi'lcult to produce satisfactory bright zinc deposits over a wide current density range from these complexfree baths using the previously effective bath additives. Additionally, the deposits from these baths are generally severely striated and/or covered with spores"in 'the medium and high current density areas. Spores" can best be described as very small, discrete, frostylooking mounds, possibly an unique type ofburnt" deposit, often accompanied by gas pitting, and completely unacceptable in bright zinc deposits.

It is an object of this invention to provide novel processes and compositions for the electrodeposition of bright to brilliant zinc plate, over a wide current density range, especially from mildly acidic, neutral, or mildly alkaline zinc plating baths, which may or may not additionally contain organic complexing agents; said deposits being free of objectionable spores and/or striations. Other objects of the invention will be apparent to those skilled in the art of bright zinc plating upon inspection of the following detailed description.

This invention relates to a method of producing bright to brilliant zinc electrodeposits over a wide current density range, free of spores and/or striations, which comprises passing current from an anode to a metal cathode for a time period sufficient to deposit a bright zinc electrodeposit upon said cathode; the current passing through an aqueous bath composition containing at least one zinc compound providing zinc ions for electroplating zinc, a suitable bath-soluble surfactant as a support or carrier and at least one compound selected from the class of compounds consisting of aromatic non-carbonyl nitrogen heterocycles. The following generalized formulae'describe typical compounds falling within the scope ofthis invention:

x Rn Ux- R, x- Y] M M 11.. x x- R I X" I X- Y. Y.

Ru Ba 1 1+ l wherein each R is independently hydrogen, alkyl, alkenyl, alkoxy, alkylamine, alkylsulfonic acid and/or salt thereof, sulfonic acid and/or salt thereof, halogen, amine, hydroxyl, mercapto, nitrile, benzyl, or phenylal- (where m is an integer 0 to 4); n is an integer t) to 3; R is a divalent alkylene, divalent alkeneylene, secondary amine. or a direct bond between two heterocyclic rings; R' is a bifunctional radical such as z is 0 or 1; Y is oxygen, allyl, propargyl, benzyl, an alkoxy group, alkyl sulfonic acid -(CH ),,-SO (where p is an integer of from I to 4), an oxyalkylsulfonic acid, quinaldinyl, halogenated alkeneyl radicals such as omatic non-carbonyl nitrogen heterocyclic compounds which'may be employed according to this invention and the radical p-phenoxybenzyl and which illustrate the generalized structural formulae given above.

/\ I Pyridine. J

2-bromopyridine. G F

2-aminopyri- I/Ci dine. \N/NH2 SO I OH: oxide.

4-picolylamine. O CH2-NH2 Ekpyridyl- @CIIr-OH carbmol. 3-pyridyl- SOsH sulfonic 0 acid.

4-cyanohi 6 CN pyridine.

4-cyano- O-N 0 CN p oxide.

" N-(2 3-dichioro-Z-D ropeny C1 C1 guinolinlum O N CH. =H iodide.

N-propargyluinolinlum gromide.

O N+-OH-CECH N -benzy1quin- Q 01- ollnium chloride.

CH 1,3-di-(4.4'- N py v i- N propane- O O Q NM qulnaldinyl I- iodide).

CH3 iHa CH: 0 O O N N C a Isoquinoline. @Q

O-HaO Isoqulnoline- N-oxide N monohy- 0i drate.

/\ 3-methyliso- IF quinoline. \/\CH3 CH2-CH=CH1 N-allyllso' qulnolinium N bromide.

N+C Hz-C CH dlbromo-2 O l I p yb- Br Br sequine- Brllnlum bromide.

' N+C H2-C C H dich10ro-2- G (g A ropenyD- l l soqulno- I- linlum iodide.

N-propar- N+-CHr-O IOH gyllso- 0 ninenium Br bromide.

/\ N-beinzyl'ilifio- +-C u no um 0 H o loride.

--Wd1fl--7 M N-(quinal- -cH,-iI din l)-pyrl-v 0 dl urn O k/ chloride.

Acridlne.

Some compounds which have given particularly out: standing results in fulfilling the objectives of this invention are:

4-cyanopyridine 4-cyanopyridine-N-oxide 3-pyridylsulfonic acid 2-mercapto-4-methylpyridine N-(2,3 dichloro-2-propenyl)-pyridinium chloride N-propargyl-2-(n-propan-3-ol)-pyridinium bromide quinoline v N-allylquinolinium bromide N-(2,3-dichloro-2-propenyl)-quinolinium iodide isoquinoline isoquinoline-N-oxide N-allyisoquinolinium bromide v N-benzylisoquinolinium chloride N -(2,3-dichloro-2-propenyl)isoquinolinium iodide acridine v A single compound or mixtures of the nitrogen heterocyclic compounds of this invention may be used in combination with other additives known to those skilled in the art of bright zinc plating to overcome deposit striations and/or spores" and-to generally increase the brightness and enhance the overall appearance and lu'ster of the zinc deposit.

The amount of heterocyclic nitrogen compound or mixtures thereof employed in the compositions of this invention is an amount sufficient to provide improved bright zinc electroplate when compared with a bath composition which is identical'lnall respects save that said bath composition contains no heterocyclic nitro gen compounds of the invention herein. The improved bright zinc electroplate deposits of the invention herein are generally characterized as showing improvement in at least one of the properties such as freedom from dullness or skip in lower current density areas, improved ductility, uniformity of lustrous deposit throughout the plating current density range and freedom from spores and/or striations. In general, amounts of heterocyclic nitrogen compounds of about 0.001 g/l-4.0 g/l (preferably about 0.005 025 g/l) may be used. v

When the aromatic non-carbonyl containing nitrogen 'heterocyclic compounds of this invention are employed in mildly acidic, neutral, or mildly basic zinc electroplating baths, they are preferably used in combination with carrier and/or support compounds known to those skilled in the art of zinc plating. These carrier and/or support compounds/are typically bath soluble polyethers, substituted polyethers and/or substituted nonaromatic nitrogen heterocyclic surfactants.

A bath soluble surfactant which may be employed in amounts of about 10-25 3/! (preferably about 2-10 g/l) in combination with the nitrogen heterocyclic compounds in amounts of about 0.001 g/l-4.0 g/l (preferably about 0.0050.25 g/l) may include aromatic ethers of aliphatic polyethers. Preferably the polyether is a polyalkoxylated alkyl phenol. Typical polyalkoxylated alkyljphenols include polyethoxylated alkyl phenols havingthe' formula:

wherein R represents an alkyl group of from 8 to 16 carbon atoms (preferably 8 or 9 carbon atoms) and j is an integer of from to 50 (preferably from about 10 to 30), and Q is hydrogen or methyl.

Other polyethers which may be employed in amounts of about 10-25 g/l (preferably about 2-10 g/l) in combination with the nitrogen heterocyclic compounds in amounts of about 0.00l-4.0 g/l (preferably about 0.005-025 g/l) may include aliphatic polyethers characterized by the following general formula:

wherein Q represents hydrogen or methyl and k is an integer of from about 7 to 100 (preferably from about 12 to 50).

Other polyethers which may be employed include alkyl polyethers of the general formula:

iii-011 'b ii b r 'ii i. i

wherein Q represents hydrogenor methyl and R5 isan alkyl group of from about 5 to 25 carbon atoms and h is an integer from about 10 to 50 (preferably about 12 to 25).

Other bath soluble surfactants which may be employed include quaternary imidazolinium compounds with the following generalized structural formula:

N -H-CHI where q is an integer of from about 50 to 5000 (preferably from about to 3500).

The nitrogen heterocyclic compounds and the polyether compounds used in combination in the novel bright zinc electroplating baths of the invention may contain inert substituents. By an inert substituent as the term is used herein is meant any bath compatible group which does not destroy, reduce, interfere with, or hinder the formation of the bright zinc electrodeposits described herein. Typical examples of inert substituents include the halogens (chloride, bromide, iodide, and fluoride); hydroxy groups, alkoxy groups (such as methoxy, ethoxy, propoxy, etc.), alkyl groups, sulfate, etc.

According to a particular aspect of the invention, a mixture of the nitrogen heterocyclic compounds and the carrier and/or support compounds (preferably a polyether) may be employed in combination with other additives. Examples of such cooperating mixtures include a 50:1 (parts by weight) combination of the reaction products of nonyl phenol with about 15 moles of ethylene oxide and a nitrogen-containing heterocyclic compound. Other suitable weight ratios of carrier and- /or support compounds (polyether) and nitrogencontaining heterocyclic compounds include weight ratios of about [00:1 to l/2:l, respectively. Mixtures of nitrogen heterocyclic compounds may also be used and wherever mixtures of nitrogen heterocycliccompounds are employed, the weight ratios referred to herein refer to the total weight of all of the nitrogen heterocyclic compounds combined.

The basis metal onto which the bright zinc deposits of this invention may be applied may include ferrous metals such as steel and cast iron; copper including its alloys such as brass, bronze, etc.; die cast metals which may bear a plate of another metal such as copper; thin coatings, e.g. of silver, nickel, or copper, on a nonconductive "mime" (sifchasa- "r'rgra offfexible plastic) which coating may be applied by chemical reductive techniques, such as electroless plating, etc.

According to another aspect of the invention the preferred operating conditions, such as pH, temperature, and current density may vary depending upon the par ticular bath composition and the nature of the article receiving the layer of bright zinc electrodeposit. in general, good, bright, zinc electrodeposits may be obtained within a specific range of operating conditions. For example, in mildly acid, neutral, or mildly basic zinc baths, when the pH is within the desired range (i.e. about l.0-10.0, preferably about 4.0-8.0) a zinc electrodeposit may attain maximum brightness and the current efficiency may also be optimized.

The bright zinc electroplating processes using the compositions of the invention may be carried out at temperatures of about l0C.-60C. (preferably 15C.-35C.) either with or without agitation. Using average current densities of 0.5-5.0 amperes per square decimeter (ASD), bright zinc electrodeposits having average thicknesses of 025-25 microns may be obtained using plating times which may average 0.5- minutes.

If necessary, agitation of the plating bath composition may be provided either by mechanical movement of the article being plated or by solution agitation during the electrodeposition. Such agitation may permit the use of high plating current densities on the article being plated.

During the plating operation, it is desirable to keep metallic contaminants at very low concentration levels in order to insure a bright zinc electrodeposit. Such. contamination from metal ions, (such as cadmium, copper, iron, and lead) may be reduced or eliminated through conventional purification methods. Other types of contaminants (such as organic contaminants) may also be eliminated or reduced by circulation of the zinc electroplating solution through a suitable filter media such as activated carbon or types of ion exchange or absorption media.

Some of the nitrogen heterocyclic compounds of this invention may have only limited solubility in aqueous solutions. In order to introduce the required amount of these materials into the plating bath, it is most advantageous to first dissolve the appropriate nitrogen heterocyclic compounds in a suitable bath soluble solvent. Such solvents include methanol, ethanol, isopropanol, ethylene glycol-monoethyl ether (i.e., cellosolve), acetone, etc. A concentration of about 25 to 50 g/l of the nitrogen heterocyclic compounds in a suitable solvent provides a satisfactory stock solution for addition to the plating bath. In this manner the nitrogen heterocyclic compounds of this invention can be easily added to the plating solution while obtaining rapid dispersion and optimum miscibility.

The following examples are submitted for the purpose of illustration only, so that those skilled in the art of zinc plating may better understand the operation of the invention. These examples are not to be construed as limiting the scope of the invention in any way.

EXAMPLE I A four liter aqueous bright zinc electroplating bath composition containing the following ingredients in the amounts indicated was prepared. L

ZnCl 40 gll NH4C| [25 g/l citric acid monohydrate 75 g/l Nl-LOH to give a pH of 4.8 Reaction product of nonylphenol and 15 moles of ethylene oxide 4 g/l J-pyridylsulfonic acid 0.3 g/l Using mild cathode rod agitation, parts were plated in the above bath at an average current density of about 2.5 asd. Excellent, uniformly bright deposits were obtained which easily accepted a subsequent clear chromate conversion coating.

EXAMPLE ll An aqueous bright zinc electroplating bath composition was prepared using the following ingredients in the amounts indicated:

ZnCl: 32 g/l NH Cl 200 g/l pH Reaction product of a mixture of linear secondary alcohols exhibiting ll to 16 carbon atoms with l2 moles of ethylene oxide 4 g/l 2-mercapto-4-methylpyridine 0.04 g/l N-(2.3-dichloro-2-propenyllisoquinolinium iodide 0.025 g/l This bath composition was operated in a 267 ml Hull cell at room temperature, using 1 ampere cell current,

- 12 a plating time of 5 minutes, mild agitation provided by a small magnetic stirrer, buffed brass cathodes and a sheet zinc anode. The resultant zinc deposit was bright across the entire density range of the panel (0-6.0 asd.) and was free of high current density spores" and/or striations.

EXAMPLE lll An aqueous bright zinc electroplating bath composition was prepared using the following ingredients in the amounts indicated:

ZnCl, 40 g/l Nfl Cl 125 g/l citric acid monohydrate NH OH to give pH 4.5 Reaction product of nonylphenol and 15 moles of ethylene oxide 4 g/l 3-pyridyl-2-ethylsulfonic acid 0.4 g/l 4-pyridyl-2-ethylsulfonic acid 0.4 gll EXAMPLE IV An aqueous bright zinc electroplating bath composition was prepared using the following ingredients in the amounts indicated:

pH 4.8 Reaction product of nonylphenol and l5 moles of ethylene oxide 4 g/l Acridine 0.05 g/l 4-cyanopyridine-N-oxide 0.4 g/l Using a 267 ml i-lull cell and the operating procedure given in Example ll, the resulting zinc deposit was bright across the entire current density range of the test panel, and was also free of spores and/or striations.

EXAMPLE V An aqueous bright zinc electroplating bath composi-- tion was prepared using the following ingredients in the amounts indicated:

ZnCI,

NH CI g/l citric acid monohydrate 75 gll NH OH sufficient to give pH 4.5

Reaction product of nonylphenol and l5 moles of ethylene oxide 4 gll l,2-di-(4,4'-pyridyl)-ethene 0.04 g/l N-(2.3-dichloro-2-prope nyl)- isoquinolinium iodide 0.01 g/l Using a 267 ml Hull cell and the operating conditions given in Example ll, the resulting zinc deposit was uniformly bright, spore free and generally excellent across the entire current density range of the test panel.

EXAMPLE Vl An aqueous bright zinc electroplating bath composition was prepared using the following ingredients in the amounts indicated:

ZnCl 40 g/l NH CI l25 g/l citric acid monohydrate 75 g/l NHqOH sufficient to give pH 75 Reaction product of nonylphenol and moles of ethylene oxide 8 gll N-benzylisoquinolinium chloride 0.025 g/l Using a 267 ml Hull cell and the operating conditions given in Example ll, the resulting zinc deposit was bright and free of spores across the entire current density range of the test panel.

EXAMPLE VII A four liter aqueous bright zinc electroplating bath composition containing the following ingredients in the amounts indicated was prepared:

ZnCl, 40 g/l NH Cl 125 g/l citric acid monohydrate 75 g/l NH OH to adjust pH to 4.5 Reaction product of nonylphenol and 15 moles of ethylene oxide 4 gll l,3-(4,4-dipyridyl)- propane-N,N"dioxide 0.4 gll N-(2,3-dichloro-2-propenyl)- isoquinolinium iodide 0.0] g/l EXAMPLE Vlll An aqueous bright zinc electroplating bath composition was prepared using the following ingredients in the amounts indicated:

ZnCl 32 g/l NH,Cl 200 gll pH as prepared 4.5 Quaternary imidazolinium compound sold as Miranol CZM-SF" by the Miranol Chemical Company. Inc. gll N-t2.2-dichloro-2-propenyl)- isoquinolinium iodide 0.025 gll Using a 267 ml Hull cell and the operating conditions given in Example II, the resulting zinc deposit was uniformly brilliant across the entire current density range of the test panel and was free of "spores and/0r striations.

EXAMPLE [X A four liter aqueous bright zinc electroplating bath composition containing the following ingredients in the amounts indicated was prepared:

ZnCl- 32 gll NH Cl 200 gll pH 4.8 ,Reaction product of nonylphenol and 15 moles of ethylene oxide 4 g/l Polyvinylpyrrolidone (M. wt. avg. 40,000) 2 g/l N-(2,3-dichloro-2-propenyl)- isoquinolinium iodide 0.02 g/l Using a small plexiglass, horizontal, hexagonal plating barrel, 12.5 cm long by 10 cm. diameter, rotating at about 5 rpm, a large number of barrel loads of steel nails (approximately 1000 sq. cm. surface area per load) were plated in the above bath composition at 10 to 20 amperes cell current for 30 minutes. The resulting zinc deposits were brilliant and lustrous as plated, free of any haziness, spores and/or striations. The deposits were subsequently rinsed and given a clear chromate conversion coating to improve their corrosion resistance as is normal in the zinc plating industry.

EXAMPLE X A four liter aqueous bright zinc electroplating bath composition was prepared using the following ingredients in the amounts indicated:

ZnCl 32 g/l NH Cl 200 g/l pH 4.8 Polyvinylpyrrolidone (M. wt. avg. 40,000) 2 gll Reaction product of nonylphenol and ii moles of ethylene oxide 4 gll N-allylisoquinolinium v l bromide 0.025 g/l A large number of parts were rack plated in this bath using cathode rod agitation of about 7 meters/min. and an average current density of about 2.0 to 3.0 asd. Plating time ranged from about 30 minutes to 2 hours. Excellent, uniformly brilliant, lustrous zinc deposits, free of haziness, spores or striations were consistently obtained from this system.

EXAMPLE XI A four liter aqueous bright zinc electroplating bath composition containing the following ingredients in the amounts indicated was prepared:

ZnCl 32 g/l NH,Cl 200 gll pH 4.8 Reaction product of a mixture of linear secondary alcohols exhibiting ll to 16 carbon atoms with l2 moles of ethylene oxide 4 gll Polyvinylpyrrolidone 2 gll N-benzylisoquinolinium chloride 0.01 gll A number of parts were plated in this bath and the resulting deposits were brilliant, lustrous and free of haze, spores" or striations. The average current densities were about 2.0 to 3.0 asd.

EXAMPLE kit A four liter aqueous bright zinc electroplating bath composition containing the following ingredients in the indicated amounts was prepared:

A number of parts were plated in the above bath at average current densities ranging from about 1.2 to 3.6

amp. per sq. decimeter. After plating, the parts were water rinsed and given a clear chromate conversion coating as is the normal practice in the zinc plating industry. The resulting zinc deposits were uniformly bright and lustrous.

EXAMPLE Xlll An aqueous bright zinc electroplating bath composition was prepared using the following ingredients in the amounts indicated:

Zn(SO NH 28 g/l Nl-l SO NH 185 g/l NH OH sufficient to give pH 4.5 Reaction product of nonylphenol and moles of ethylene oxide 4 g/l Polyvinylpyrrolidone (Molecular weight avg.

40,000) 2 g/l N-(2,3-dichloro-2-propeny1)- isoquinolinium iodide 0.025 g/l Using a 267 mll-iull cell and tli operatiiig condi tions given in Example II, the resulting zinc deposit was uniformly bright across the entire test panel and was free of spores and/or striations.

EXAMPLE XIV An aqueous bright zinc electroplating bath composition was prepared using the following ingredients in the amounts listed:

ZnSO,-7H,O 100 gll NH,C1 100 g/l Citric acid monohydrate 100 g/l NH OH sufficient to give pH 8.0 Reaction product of nonylphenol and 15 moles of ethylene oxide 4 gll lsoquinoline-N-oxide monohydrate 0.025 g/l Using a 267 ml Hull cell and the operating conditions given in Example 11, the resulting zinc deposit was lustrous and bright as well as free of striations or spores across the entire current density range of the test panel.

Although this invention has been illustrated by referonce to specific embodiments. modifications thereof which are clearly within the scope of the invention will be apparent to those skilled-imthe-art.

1 claim:

l. A method of producing bright, or brilliant zinc electrodeposits free of spores" and/or striations over a wide current density range which comprises passing current from an anode to a metal cathode through an aqueous bath composition having a pH of 1.0 to 10.0 and containing at least one zinc compound providing zinc ions for electroplating zinc,

a. 1.0 gram per liter to 25 grams per liter of at least 16 one bath soluble surfactant selected from the group consisting of bath soluble polyethers, substituted polyethers, and substituted non-aromatic nitrogen heterocyclic surfactants selected from the group consisting of quaternary imidazolinium compounds and polyvinylpyrrolidone polymers; and

b. 0.001 gram per liter to 4.0 grams per liter of at least one aromatic, non-carbonyl, nitrogencontaining heterocyclic compound for a time period sufficient to deposit a bright zinc electrodeposit upon said cathode.

2. The method as claimed in claim 1 wherein at least one nitrogen-containing heterocyclic compound is of the formula wherein each R is independently hydrogen, alkyl, alkenyl, alkoxy, alkylamine, alkysulfonic acid or salts thereof, sulfonic acid or salts thereof, halogen, amine, hydroxyl, mercapto, nitrile, benzyl, or phenylalkyl (where m is an integer 0 to 4 nis anin teger 0 to 3; z is 0 or 1; Y is oxygemallyl, propargyl. benzyl, an alkoxy group, alkyl sulfonic acid -(CH ),,-SO (where p is an integer of from 1 to 4), an oxyalkylsulfonic acid, quinaldinyl. p-phenoxybenzyl, or a halogenated alkeneyl radical, and X represents an anionic radical or the anionic moiety of Y or R-provided that when Y is oxygen X is'absent.

3. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is isoquinoline.

4. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is isoquinoline-N-oxide.

5. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is N- allylisoquinolinium bromide.

6. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is N- (2,3-dichloro-2-propenyl)-isoquinolinium iodide.

7. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is N- benzylisoquinolinium chloride.

8. The method as claimed in claim 1 wherein at least one bath-soluble surfactant is a polyether of the formula:

wherein R, is an alkyl group of 8-16 carbon atoms.j is an integer 5-50 and Q is hydrogen or methyl.

9. The method as claimed in claim 1 wherein at least one bath-soluble surfactant is a polyvinylpyrrolidone of the formula:

where q is an integer of from about 50 to 5000.

10. A composition for providing bright, or brilliant zinc electrodeposits free of spores and/or striations 1 over a wide current density range which comprises an aqueous bath composition having a pH of 1.0 to 10.0 and containing at least one zinc compound providing zinc ions for electroplating zinc,

a. 1.0 gram per liter to 25 grams per liter of at least one bath-soluble surfactant selected from the group consisting of bath-soluble polyethers, substituted polyethers, and substituted non-aromatic nitrogen heterocyclic surfactants selected from the group consisting of quaternary imidazolinium compounds and polyvinylpyrrolidone polymers; and

b. 0.001 gram per liter to 4.0 grams per liter of at least one aromatic, non-carbonyl, nitrogencontaining heterocyclic compound.

11. A composition as claimed in claim wherein at least one nitrogen-containing heterocyclic compound is of the formula:

wherein each R is independently hydrogen, alkylfalk enyl, alkoxy, alkylamine, alkylsulfonic acid or salts thereof, sulfonic acid or salts thereof, halogen, amine, hydroxyl, mercapto, nitrile, benzyl, or phenylalkyl (where m is an integer O to 4)j n is an integer 0 to 3 z is 0 or 1; Y is oxygen, allyl, propargyl, benzyl, an alkoxy group, alkyl sulfonic acid (CH ),,SO p is an integer of from 1 to 4), and oxyalkylsulfonic acid,

18 quinaldinyl, p-phenoxybenzyl or a halogenated alkeneyl radical, and X represents an anionic radical or the anionic moiety of Y or R provided that when Y is oxygen X is absent.

12. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is isoquinoline.

13. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound 0 is isoquinoline-N-oxide.

14. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is N-allylisoquinolinium bromide.

15. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is N-(2,3-dichloro-2-propenyl)-isoquinolinium iodide.

16. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is N-benzylisoquinolinium chloride.

17. A composition as claimed in claim 10 wherein at least one bath-soluble surfactant is a polyether of the formula:

least one bath-soluble surfactant is a polyvinylpyrrolidone of the formula:

where q is an integer 5? rmrfl'abbut 50 65000. 

2. The method as claimed in claim 1 wherein at least one nitrogen-containing heterocyclic compound is of the formula
 3. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is isoquinoline.
 4. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is isoquinoline-N-oxide.
 5. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is N-allylisoquinolinium bromide.
 6. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is N-(2,3-dichloro-2-propenyl)-isoquinolinium iodide.
 7. The method as claimed in claim 2 wherein at least one nitrogen-containing heterocyclic compound is N-benzylisoquinolinium chloride.
 8. The method as claimed in claim 1 wherein at least one bath-soluble surfactant is a polyether of the formula:
 9. The method as claimed in claim 1 wherein at least one bath-soluble surfactant is a polyvinylpyrrolidone of the formula:
 10. A composition for providing bright, or brilliant zinc electrodeposits free of ''''spores'''' and/or striations over a wide current density range which comprises an aqueous bath composition having a pH of 1.0 to 10.0 and containing at least one zinc compound providing zinc ions for electroplating zinc, a. 1.0 gram per liter to 25 grams per liter of at least one bath-soluble surfactant selected from the group consisting of bath-soluble polyethers, substituted polyethers, and substituted non-aromatic nitrogen heterocyclic surfactants selected from the group consisting of quaternary imidazolinium compounds and polyvinylpyrrolidone polymers; and b. 0.001 gram per liter to 4.0 grams per liter of at least one aromatic, non-carbonyl, nitrogen-containing heterocyclic compound.
 11. A composition as claimed in claim 10 wherein at least one nitrogen-containing heterocyclic compound is of the formula:
 12. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is isoquinoline.
 13. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is isoquinoline-N-oxide.
 14. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is N-allylisoquinolinium bromide.
 15. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is N-(2,3-dichloro-2-propenyl)-isoquinolinium iodide.
 16. A composition as claimed in claim 11 wherein at least one nitrogen-containing heterocyclic compound is N-benzylisoquinolinium chloride.
 17. A composition as claimed in claim 10 wherein at least one bath-soluble surfactant is a polyether of the formula:
 18. A composition as claimed in claim 10 wherein at least one bath-soluble surfactant is a polyvinylpyrrolidone of the formula: 